1. Characterization of Powders, Porous Solids and Suspensions Lecture 8

4. What is Particle Size? SEM of real ibuprofen particles

6. Different Equivalent Spheres

9. Particle Size by Direct Observation Google for ImageJ

16. Schematics of Zetasizer Nano

17. Measurement of Porosity and Specific Surface Area by Gas Adsorption

19. Measure of Porosity Pore size and its distribution Specific Surface Area, m 2 /g = Porosity There are three parameters used as a measure of porosity; specific surface area, specific pore volume or porosity, and pore size and its distribution. Mass of the solid, g Total surface area, m 2 Specific Pore volume, cm 3 /g Mass of the solid, g Total pore volume, cm 3 = Porosity, % = Volume of solid (including pores) Volume of pores X 100

20. Concept of Porosity: Open vs. Closed Pores Dead end (open) Closed Inter-connected (open) Passing (open) F. Rouquerol, J. Rouquerol, K. S. W. Sing, Adsorption by Powders and Porous Solids, Academic Press, 1-25, 1999 Open pores are accessible whereas closed pores are inaccessible pores. Open pores can be inter-connected, passing or dead end.

21. Size of Pores (IUPAC Standard) 2 nm 50 nm Micropores Mesopores Macropores Zeolite, Activated carbon, Metal organic framework Mesoporous silica, Activated carbon Sintered metals and ceramics Porous material are classified according to the size of pores: material with pores less than 2 nm are called micropores, materials with pores between 2 and 50 nm are called mesopores, and material with pores greater than 50 nm are macrospores Sing, K. S. W. et al. Reporting Physisorption Data for Gas/Solid Systems. Pure & Appl. Chem. 57, 603-619 (1985).

22. Shapes of Pores Conical Interstices F. Rouquerol, J. Rouquerol, K. S. W. Sing, Adsorption by Powders and Porous Solids, Academic Press, 1-25, 1999 Slits Cylindrical Spherical or Ink Bottle Pore Shapes

23. Experimental Techniques

24. Techniques for Porosity Analysis Mercury porosimetry TEM SEM Small angle X-ray scattering Small Angle Neutron scattering Gas adsorption Techniques

31. Theory of Adsorption

32. Adsorption Process Adsorption is brought by the forces acting between the solid and the molecules of the gas. These forces are of two kinds: physical (physiosorption) and chemical (chemisorption) Adsor bent - the solid where adsorption takes place Adsor bate - the gas adsorbed on the surface of solids Adsor ptive - adsorbate before being adsorbed on the surface

33. Physisorption vs Chemisorption http://www.soton.ac.uk PHYSISORPTION CHEMISORPTION WEAK, LONG RANGE BONDING Van der Waals interactions STRONG, SHORT RANGE BONDING Chemical bonding involved. NOT SURFACE SPECIFIC Physisorption takes place between all molecules on any surface providing the temperature is low enough. SURFACE SPECIFIC E.g. Chemisorption of hydrogen takes place on transition metals but not on gold or mercury. Δ H ads = 5 ….. 50 kJ mol-1 Δ H ads = 50 ….. 500 kJ mol -1 Non activated with equilibrium achieved relatively quickly. Increasing temperature always reduces surface coverage . Can be activated, in which case equilibrium can be slow and increasing temperature can favour adsorption. No surface reactions. Surface reactions may take place:- Dissociation, reconstruction, catalysis. MULTILAYER ADSORPTION BET Isotherm used to model adsorption equilibrium. MONOLAYER ADSORPTION Langmuir Isotherm is used to model adsorption equilibrium.

35. Adsorption Process Adsor bent Adsor bate S. Lowell & J. E. Shields, Powder Surface Area and Porosity, 3rd Ed. Chapman & Hall, New York, 1991 Equation of adsorption isotherm

41. Gas Sorption: Hysteresis V a Type A Cylindrical Slits Type B Type C Type E Conical Bottle neck 1 P/P o 1 P/P o 1 P/P o Type D 1 P/P o 1 P/P o

44. Specific Surface Area Calculation At least three data points in the relative pressure range 0.05 to 0.30 P/P o 1 V[(P o /P)-1] 0-1 0-2 0-3

46. Pore Size Distribution V a Pore diameter, d Narrow pore size distribution Pore diameter, d Multimodal pore size distribution The distribution of pore volume with respect to pore size is called a pore size distribution. V a Broad pore size distribution Unimodal pore size distribution

49. Pore Size: Kelvin Equation Actual radius of the pore Kelvin radius of the pore Thickness of the adsorbed layer Prior to condensation, some adsorption has taken place on the walls of the pore, r k does not represent the actual pore radius. Adsorbed layer

51. Porosity Analyzer Outgassing station Analysis station Liquid nitrogen bath

52. Steps for Measurement 3. Interpretation 2. Adsorption Analysis 1. Sample Preparation

55. Interpretation OUTPUT Points P/P o Volume adsorbed 1 2 3 Weight of sample Pore shape Specific surface area Pore volume Pore size & distribution Results